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<DIV style="TEXT-ALIGN: justify"><SPAN class=postbody>William Livingston e Matt
Penn, investigadores do Observatório Nacional Solar – Tucson: EUA - dizem que o
nosso Sol, a partir de 2015, poderá perder as suas manchas solares, denotando
menos actividade, o que poderá levar a uma nova pequena idade do gelo - como no
Maunder Minimum (Mínimo de Maunder), entre 1645 e 1715 quando a actividade de
manchas solares reduziu-se drasticamente, gerando na Terra uma redução dramática
da temperatura. </SPAN><SPAN class=postbody>No continente europeu e América do
Norte registraram-se temperaturas baixíssimas, provocando o congelamento de
grandes cursos de rios que normalmente não passam por essa situação.
</SPAN><SPAN class=postbody></SPAN><SPAN class=postbody>O nome
“Maunder” deve-se ao astrónomo inglês E. W. Maunder (1851-1929) do
Observatório de Greenwich, que o relatou quando estudava os
registos históricos sobre o Sol</SPAN></DIV></DIV>
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<DIV class="post-body entry-content"></SPAN></FONT></SPAN><STRONG><FONT
size=6>Are sunspots disappearing?</FONT></STRONG></DIV></DIV></DIV></DIV>
<P><FONT face=Verdana><STRONG>Nasa</STRONG> report that the sun is in the pits
of the deepest solar minimum in nearly a century. Weeks and sometimes whole
months go by without even a single tiny sunspot. The quiet has dragged out for
more than two years, prompting some observers to wonder, <EM><STRONG>are
sunspots disappearing?</STRONG></EM></FONT></P>
<P><FONT face=Verdana>"Personally, I'm betting that sunspots are coming back,"
says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson,
Arizona. But, he allows, "there is some evidence that they won't."</FONT></P>
<P><FONT face=Verdana>Penn's colleague Bill Livingston of the NSO has been
measuring the magnetic fields of sunspots for the past 17 years, and he has
found a remarkable trend. Sunspot magnetism is on the decline.</FONT></P>
<P><FONT face=Verdana>While most researchers measure the splitting of spectral
lines in the visible part of the sun's spectrum, Livingston decided to try an
infra-red spectral line. Infrared lines are much more sensitive to the Zeeman
effect and provide more accurate answers. Also, he dedicated himself to
measuring a large number of sunspots—more than 900 between 1998 and 2005 alone.
The combination of accuracy and numbers revealed the downturn.</FONT></P>
<P><FONT face=Verdana>"According to our measurements, sunspots seem to form only
if the magnetic field is stronger than about 1500 gauss," says
Livingston.</FONT></P>
<P><FONT face=Verdana>"If the current trend continues, we'll hit that threshold
in the near future, and solar magnetic fields would become too weak to form
sunspots."</FONT></P>
<P><FONT face=Verdana>"This work has caused a sensation in the field of solar
physics," comments NASA sunspot expert David Hathaway, who is not directly
involved in the research. "It's controversial stuff."</FONT></P>
<P><FONT face=Verdana>If sunspots do go away, it wouldn't be the first
time.<BR>In the 17th century, the sun plunged into a 70-year period of
spotlessness known as the <EM><STRONG>Maunder Minimum</STRONG></EM> that still
baffles scientists. The sunspot drought began in 1645 and lasted until 1715;
during that time, some of the best astronomers in history (e.g., Cassini)
monitored the sun and failed to count more than a few dozen sunspots per year,
compared to the usual thousands.</FONT></P>
<P><FONT face=Verdana>"Whether [the current downturn] is an omen of long-term
sunspot decline, analogous to the Maunder Minimum, remains to be seen,"
Livingston and Penn caution in a recent issue of EOS. "Other indications of
solar activity suggest that sunspots must return in earnest within the next
year."</FONT></P>
<P><FONT face=Verdana>Whatever happens, notes Hathaway, "the sun is behaving in
an interesting way and I believe we're about to learn something new."</FONT></P>
<P><FONT face=Verdana>Read the full NASA report at</FONT></P>
<DIV><A
href="http://science.nasa.gov/headlines/y2009/03sep_sunspots.htm?list130845"
target=_blank><FONT
face=Verdana>http://science.nasa.gov/headlines/y2009/<BR>03sep_sunspots.htm?list130845</FONT></A>
<BR></DIV>
<DIV><FONT face=Verdana>Fontes: Blog Ano Zero e Southgate Amateur Radio
Club.</FONT></DIV></BODY></HTML>